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I'm at a loss right now, can't pin point where the problem may be so I'll run you guys through real quick of my situation.

I have a 1999 Civic EX EJ8, coupe.
I got it recently from my cousin; it sat for 2 years but started on the first try. I've been fixing it up so it is my daily right now.

I've had the car for about 2 months and up until last week I lost heat in the cabin; only blowing cold.
1. I checked my heater hoses, heat is going through both inlet to Heater core, and back out to the outlet.
2. No loss of fan speed whatsoever when I change fan speed. (Heater blower motor ok then?)
3. Temp sensor is working fine, haven't over heated.
4. Checked fuses and replaced them.
5. The heater blower Motor Relay works

Anything else I should check? I think the culprit is heater blower motor, heater blower resistor, or even just a coolant flush. Let me know your thoughts, thanks guys.

 
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Also, checked coolant reservoir - full. Took off radiator cap and coolant is to the neck.

 
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https://www.civicforums.com/forums/3...reference.html

looks like this applies to 6th gen too...

headgasket

 
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Replace your coolant with water + 2 large spoons Disodium EDTA. Drive it for a month and it will take off the deposits from everything in contact. Beware the solution will freeze in cold weather.

 
Rep Power: 210

Cabin heat is based on engine heat of which pressure is a part of.
Trapped air in coolant system, low coolant, blocked heater core (under dash), a thermostat stuck open, malfunctioning heater valve, heat and breached head gasket can all present as cabin air heat loss.

Start by bleeding air from coolant. Raise front end on Jack's, turn climate control to Max heat with fan off, let engine from cold start idle to operating temp with rad cap off (and optional spill-proof funnel) to bleed air bubbles until radiator fans engage (roughly 20-30 minutes). Add coolant mix as needed to keep radiator full and reservoir somewhere between min and max. Let engine cool and check radiator and reservoir levels..fill as needed.

 
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Appreciate all your replies, I'll post what I find!